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Car Forum / Driving, Maintenance, Tuning / RVs / December 200790 ohm sending unit on aprox 200 ohm stock guage
I just replaced my sending unit with a 90 ohm GM replacement unit from JC whitney... at full on the unit the guage reads just under 1/2 tank.. proprtionally down to empty.... I am asuiming the guage wants to see 200 ohms at full ...my question is this... how can i wire a resistor to double the resistance so i dont have to drop the tank again? what size should i use? should i go in series or tip to ring? thanks >I just replaced my sending unit with a 90 ohm GM replacement unit from > JC whitney... at full on the unit the guage reads just under 1/2 > tank.. proprtionally down to empty.... I am asuiming the guage wants > to see 200 ohms at full ...my question is this... how can i wire a > resistor to double the resistance so i dont have to drop the tank > again? what size should i use? should i go in series or tip to ring? You're not going to solve your problem by throwing a resistor at it. Say for example your math is correct at this point: If you put a 100 ohm resistor is series your gauge will now see a minimum of 100 ohms, and up to 190 ohms, where it wants to see something around 0 to 200 ohms. It will shift the guage so that you see from full to half a tank, at which point the tank will be empty. If you add a parallel resistor it will reduce the total resistance that the guage sees. TB >>I just replaced my sending unit with a 90 ohm GM replacement unit from >> JC whitney... at full on the unit the guage reads just under 1/2 [quoted text clipped - 12 lines] > > TB Instead of putting a resistor on the sender side of the circuit, put the resistor between the meter and 12 volt side. Place it in parallel with the existing resistor and it will bring the node voltage of the meter/sensor voltage divider back to the correct level and it will respond correctly. Steve > Instead of putting a resistor on the sender side of the circuit, put the > resistor between the meter and 12 volt side. Place it in parallel with the > existing resistor and it will bring the node voltage of the meter/sensor > voltage divider back to the correct level and it will respond correctly. > > Steve Reference circuit: http://www.6066gmcguy.org/Electrical-02.htm In this circuit the gauge acts as an ammeter, not a voltmeter. You would have to place a resistor across the gauge to shunt some current that would flow through the gauge. The 90 ohm sender draws too much current for the gauge. You would have to measure the resistance of the gauge and from that figure out the resistor. If you know the resistance of the gauge I would be willing to calculate the resistance value for you. This is good if your meter acts as an ammeter. Do you have a circuit for it? Your gauge would draw about twice as much current as a 200 ohm one. I would put a resistor of equal value to the meter resistance across the meter, or a resistor of slightly less resistance. Steve > > Instead of putting a resistor on the sender side of the circuit, put the > > resistor between the meter and 12 volt side. Place it in parallel with the [quoted text clipped - 19 lines] > > Steve Im guessing at full the guage needs about 210 ohms.. and at empty 0 ohms... like i said i just put in a brand new 90 ohm sending unit... >> > Instead of putting a resistor on the sender side of the circuit, put >> > the [quoted text clipped - 30 lines] > Im guessing at full the guage needs about 210 ohms.. and at empty 0 > ohms... like i said i just put in a brand new 90 ohm sending unit... The sending unit is 90 ohms. But you have to get the correct amount of current through the gauge for it to read correctly. A 90 ohm sender draws more current than a 200 ohm sender. This sender draws 2.2 times more current through the gauge than your old one. A resistor must be placed across the gauge to reduce the current flowing through it. The gauge has an intrinsic resistance probably about 5 ohms or so. So a resistance of a value equal to the gauge resistance placed across the gauge will reduce the gauge current by 1/2. The resistance of the sending unit is alone is not sufficient to determine the value of the resistor to be placed in shunt with the gauge. You can place a 200 ohm potentiometer across the gauge and dial in the correct value. Most potentiometers have three legs so the center leg will have to be connected to one of the other legs. Steve > >> > Instead of putting a resistor on the sender side of the circuit, put > >> > the [quoted text clipped - 47 lines] > > - Show quoted text - Kool beans.. can u suggest a radio shack part number that will be sufficient? Radio shack is right next to me..... >> >> > Instead of putting a resistor on the sender side of the circuit, put >> >> > the [quoted text clipped - 61 lines] > Kool beans.. can u suggest a radio shack part number that will be > sufficient? Radio shack is right next to me..... Caveat: We do not know the resistance of your gauge. When the sender reads zero ohms it should not draw lots of current, so the gauge resistance may be higher, which makes sense. Try this and see what happens: http://www.radioshack.com/product/index.jsp?productId=2062354&cp=&sr=1&origkw=po tentiometer&kw=potentiometer&parentPage=search It's a 10K value and may be touchy to get the setting correct. Hopefully your gauge resistance is on the order of 1K or more which should make the adjustment easier. Steve > >> "st" <shane...@gmail.com> wrote in message > [quoted text clipped - 81 lines] > > - Show quoted text - ok i got the pot installed like u said .. middle and side to one side of sending unit.. and a lone side to ground of sending unit... my ohm meter reads 90 at full and 0 at empty still... the thing i does do when adjusted is lower the full down to nothing if i wish.... that would be great if my sending unit was a 250 ohm at full lets say and i needed to make full read 90 for my guage.......did i connect it correttly? should i run it in series instead of paralell???? >> >> "st" <shane...@gmail.com> wrote in message >> [quoted text clipped - 103 lines] > needed to make full read 90 for my guage.......did i connect it > correttly? should i run it in series instead of paralell???? The potentiometer goes across the meter (gauge) in the dashboard, not across the sending unit. Read my posts over very carefully. Perhaps someone else can help explain this all better than I can. Help please! Steve > >> "st" <shane...@gmail.com> wrote in message > [quoted text clipped - 117 lines] > > - Show quoted text - Steve, I just did as u said and the potentiometer burnt up..... I guess my guage is the culprit.... It reads just under 1/2 tanks at full on the sending unit... i know all this because i have a spare sendning unit out side the tank im using for testing purposes.....I guess i should install an aftermarket bolt on 90 ohm guage at this point dont you think?? thanks for all your help... >> >> "st" <shane...@gmail.com> wrote in message >> [quoted text clipped - 143 lines] > install an aftermarket bolt on 90 ohm guage at this point dont you > think?? thanks for all your help... Go with the 200 ohm sender. > >> "st" <shane...@gmail.com> wrote in message > [quoted text clipped - 151 lines] > > - Show quoted text - Steve.. im getting close.. i pulled the orig guage out of the cluster..... there are 3 poles 2 on the sides and one in the middle bottom.. with an ohm meter i get 87 ohms on each side post ... about 187 with bottom post and 1 side post.... maybee my wire in the rv is goofed.... everyone i speak to says 1984 p-30 is 90 ohm sender and 90 ohm guage... so could it be the sender wire is possibly touching ground somewhere??? thanks and thanks for ur patience.... > > "st" <shane...@gmail.com> wrote in message > [quoted text clipped - 166 lines] > > - Show quoted text - I tested the beige wire from the sender in the cluster wiring and got nothing touching ground.... meanwhile if i turn on the key with the sender in full position it shows 87 ohms .. when key is off it shows 90 ohms.... > > "st" <shane...@gmail.com> wrote in message > [quoted text clipped - 129 lines] > install an aftermarket bolt on 90 ohm guage at this point dont you > think?? thanks for all your help... I see what you probably did. If your tank was near empty the bypass shunt around your Full side electromagnet (the internal tank variable resistor) was close to zero ohms because the system wanted all the current going through the Empty side electromagnet. Now, if you put the potentiometer across the electromagnet on the empty side (correctly I might add only if the tank were full) and lowered the resistance (you'd want to start with that at full resistance) as you lowered the resistance the current increased because it was the only thing between the battery and ground (except for the tank internal variable resistance which would be almost zero with a low level of fuel). As the potentiometer approached zero resistance the current across the battery terminals did exactly what would be expected if it were shown a short. The potentiometer adjustment needs to be done with a full tank because you'd be adjusting the needle from halfway at a full tank to full at a full tank. By the way, I'm made that very mistake and burned up a variable resistor in an application years ago. Once the needle reaches Full, remove the pot and measure it then put that value in place across the meter (should go without saying I suppose). Bill > >> > Instead of putting a resistor on the sender side of the circuit, put > >> > the [quoted text clipped - 47 lines] > > - Show quoted text - Quite a bit of this is correct --- but the resistor must be placed in series with the gauge/sender to increase resistance. Rt=R1+R2+R3.... Resistance in parallel will ALWAYS be less than the value of the smallest resistance. 1/RT=1/R1+1/R2+1/R3 Good Luck, Mark > >> > Instead of putting a resistor on the sender side of the circuit, put > >> > the [quoted text clipped - 45 lines] > > Steve I see what you're saying. Looking at the meter sketch from the earlier link, putting a resistor across the electromagnet that draws the needle toward empty will allow two paths of current and all that current will go through the electromagnet on the full side when the tank is full and the resistance to ground (path shunting the electromagnet on the Full side) via the meter is high. So, with a full tank put a decade resistance box across the meter to the high leg and lower the resistance until the meter reads full. When the tank is empty the path through the gauge to ground will have a very low resistance and the electromagnet on the high side sees no current while the magnet on the empty side sees all the current it needs to show empty. The gauge would swing fully between E and F but, and not that it matters much, will the reading be linear? Bill On Nov 26, 11:37 pm, "Technobarbarian" <Technobarbarian- ztopz...@gmail.com> wrote: > >I just replaced my sending unit with a 90 ohm GM replacement unit from > > JC whitney... at full on the unit the guage reads just under 1/2 [quoted text clipped - 12 lines] > > TB I don't know if changing the resistance will work or not, but I do know that your theory is wrong. Resistance in series is additive. Mark > On Nov 26, 11:37 pm, "Technobarbarian" <Technobarbarian- > ztopz...@gmail.com> wrote: [quoted text clipped - 21 lines] > I don't know if changing the resistance will work or not, but I do > know that your theory is wrong. Resistance in series is additive. I thought that was what I said. TB On Nov 28, 11:06 pm, "Technobarbarian" <Technobarbarian- ztopz...@gmail.com> wrote: > > On Nov 26, 11:37 pm, "Technobarbarian" <Technobarbarian- > > ztopz...@gmail.com> wrote: [quoted text clipped - 30 lines] > > - Show quoted text - -------------------------------------------- Yup -- I just re-read your post, and you were correct. Sorry, Mark > On Nov 28, 11:06 pm, "Technobarbarian" <Technobarbarian- > [quoted text clipped - 45 lines] > > - Show quoted text - I am now looking for a 90 ohm replacement guage for my stock cluster....if anyone knows where i can find the stock 90 ohm guage that goes in this cluster .. http://www.custominstrumentpanels.com/images/p-30oldf.jpg let me know.. thanks... for everyones help.. > > On Nov 28, 11:06 pm, "Technobarbarian" <Technobarbarian- > [quoted text clipped - 50 lines] > that goes in this cluster ..http://www.custominstrumentpanels.com/images/p-30oldf.jpg > let me know.. thanks... for everyones help.. Okay guys, now I'm just checking out the gauges on my new old Lindy. The gas gauge settles at about a third of a tank. The oil gauge had been fudged. It say way high. The needle had been popped off and repositioned so as to show high pressure. I reset the needle and now it's not real good. Anyway, that makes me wonder about the gas gauge. Correct me if I'm wrong but since it reads a third of a tank, the three terminals will read battery voltage, a mid-range voltage and ground. If I jump ground to the mid-range terminal the gas gauge should read zero, if I change the jumper from ground to battery voltage and mid-range terminal the meter should read full. If you agree I'll give it a go tomorrow. Next, how do I go about ascertaining the true oil pressure? How concerned should I be about low oil pressure? If I raise the RPM's the needle moves a measurable distance. It's not the time of year to drop the pan and change bearings. Bill |
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